THE ARCH OF THE AORTA 



531 



second right costal cartilage to the lower border of the fourth thoracic vertebra. 

 Attached to the concavity of the arch, just beyond the origin of the left sub- 

 clavian artery, is the ligamentum arteriosum (vestige of the dorsal part of the 

 left sixth arch). Between the left subclavian artery and the hgamentum arterio- 

 sum there is sometimes a definite constriction of the arch (isthmus aortae) situated 

 opposite the third thoracic vertebra. When the isthmus is well marked, it is 

 succeeded by a dilatation (aortic spindle) which begins in the neighbourhood of 

 the ligamentum arteriosum and passes over into the descending aorta. Passing 

 under the arch are the left bronchus, the right pulmonary artery, and the left 

 recurrent (inferior laryngeal) nerve. It measures about 4.5 cm. (If in.). 



Fig. 442. — The Thoracic and Abdominal Aorta. 



Right common carotid 



artery 

 Right internal jugular 



vein 



Right lymphatic duct 



Innominate artery 



Right vagus nerve 



Right innominate vein 



Internal mammary vein 



Trunk of the pericardiac 



and thymic veins 



Superior vena cava 



Azygos vein 



Hemiazygos vein, cross- 

 ing spine to enter vena 

 azygos 



Hepatic veins 



Inferior vena cava 



Right inferior phrenic 

 artery 

 Coeliac artery 



Right middle suprarenal 

 artery 



Right internal spermatic 

 artery 



Right spermatic vein 



Left common carotid 



artery 

 Left vagus nerve 



Thoracic duct 



Left innominate vein 



Left subclavian artery 



Left superior intercostal 

 vein 



Recurrent (laryngeal) 

 nerve 



Accessory hemiazygos 



vein 

 (Esophagus 



Left upper azygos vein 



(Esophageal branches 

 from aorta 



Hemiazygos vein 



Thoracic duct 



Left inferior phrenic 

 artery 



Left middle suprarenal 



artery 

 Receptaculum chyli 



Superior mesenteric 

 artery 



Left ascending lumbar 



vein 



Left internal spermatic 



artery 



Inferior mesenteric 

 artery 



Relations.— In front and to the left, it is slightly overlapped by the right pleura aiid lung, 

 and to a greater extent by the left pleura and lung. It is crossed in the following order from 

 right to left, by the left phrenic nerve, by the cardiac branches of the vagus nerve, the cardiac 

 branches of the sympathetic nerve, by the left vagus nerve, and by the left superior intercostal 

 vein as it passes up to the left innominate vein. . 



Behind and to the right are the trachea, the esophagus, the thoracic duct, the deep cardiac 

 plexus which is situated on the trachea just above its bifurcation, and the left recurrent (inferior 

 laryngeal) nerve. . . i xr. 



Above it are the three chief branches for the head, neck, and upper extremities, namely, the 

 innominate, the left carotid, and the left subclavian arteries, and the left innominate vem. 



